Technical Abstract:
The avian influenza (AI) vaccine designated TROVAC-AIV H5 (TROVAC) contains a live fowlpox (FP) recombinant (recFP), expressing the hemagglutinin (HA) gene of an AI H5 subtype isolate. This recombinant vaccine received a conditional license in US in 1998 and 1.6 billion doses were used since then in Mexico, Guatemala and El Salvador. One injection of TROVAC protects chickens against AI-induced mortality and morbidity for at least 20 weeks, and significantly decreases shedding after challenge with a wide panel of H5-subtype AI strains. Recently, excellent protection was demonstrated against 2003 and 2004 Asian highly pathogenic H5N1 isolates. Whereas TROVAC AI H5 efficacy is not inhibited by anti-AI or anti-FP maternal antibodies (passive immunity), it is significantly decreased in chickens previously vaccinated or infected with FP (active immunity). Advantages of TROVAC vaccine over inactivated AI vaccines are: (1) administration at 1 day of age and early onset (1 week) of protection, (2) easy monitoring of AI infection in vaccinated flocks with AGP and ELISA (DIVA tests). These features make TROVAC the ideal AI vaccine for hatcheries. RecFP expressing HA from 3 lineages of H7 subtype (Eurasian, American and Australian) were also tested for efficacy against an HPAI Eurasian HPAI H7N1. Only the recFP expressing the Eurasian H7 gene provided sufficient protection indicating that the broadness of protection induced by recFP may be more restricted for H7 than for H5. The fowlpox vector technology can also be used for the production of an emergency vaccine: once the HA sequence of an emerging AI virus is known, recFP can be rapidly generated. TROVAC has recently been shown to be immunogenic in cats, and could therefore also be considered for use in mammals.